As a prior art technique for a pad electrode the applicant of the present application has proposed in JP-UM-63-170944(A) a pad electrode consisting of an Al electrode, on which a Cu thin film is disposed.
The pad electrode thus constructed is reliable against various heat cycles after wire bonding using an Au line and excellent.
On the other hand, as a prior art technique for a bump electrode for wireless bonding, there are known electrode structures by the flip chip method and the TAB (Tap Automated Bonding) method. As an example thereof FIG. 4 shows an electrode structure by the TAB method.
In the Figure, reference numeral 11 is an Si substrate; 12 is an SiO.sub.2 oxide film; 13 is an Al pad; 14 is a bonding layer; 15 is a barrier metal; and 16 is a bump. For the bonding layer Ti and Cr; for the barrier metal W, Pt, Ag, Ni and Cu; and for the bump Au, Cu and (Pb/Sn) solder are used principally. Further plating, the vacuum evaporation method, the sputtering method, the CVD method, etc. are used for the formation of the bonding layer 14 and the barrier metal 15 and the bump is formed by plating.
However, in the pad electrode structure described above, the Cu thin film disposed on the Al electrode has a drawback that Cu is oxidized in an oxidizing atmosphere so that wire bonding becomes impossible or initial strength is lowered, because it is heated at wire bonding.
On the other hand, in the bump electrode structure, bonding is effected by the thermal pressure bonding method at about 500.degree. C. As a material for the bump, recently Cu, which is not expensive, is used for the reason that Au is expensive so that fabrication cost is too high. In the case where Cu is used, it is easily oxidized by heat at the bonding or heat, which it receives between the formation of the bump and the bonding, which makes the bonding impossible or gives rise to lowering in initial strength. For this reason, after the formation of the bump the atmosphere at the bonding should not be oxidizing, but it should be inert gas atmosphere such as N.sub.2 gas, Ar gas, etc.